Clamping fixture for detachably fixing a tool, in particular a disc

ABSTRACT

A clamping fixture for detachably fixing a tool to a driven spindle and comprising a flange for applying a clamping force to the tool and axially displaceable relative the driven spindle and coupled to the driven spindle for transmitting a torque thereto, a supporting element for securing the flange against axial displacement relative to the spindle to prevent the flanges from applying a damping force to the tool, the supporting element comprising an annular nut member displaceably mounted on the spindle adjacent an end of the flange which is remote from the tool, and having a right-hand coarse thread to be screwed onto the threaded portion with an external coarse thread of the spindle, a torsion spring for coupling the annular nut member to the flange, and a locking device for preventing rotation of the annular nut member upon actuation of the locking device.

BACKGROUND OF THE INVENTION

The invention starts from a clamping fixture for detachably fixing atool, in particular a disc and comprising two flanges for clamping thetool therebetween and of which one flange is axially displaceable on thespindle. Clamping fixtures, in particular for disc-shaped tools aresuitable particularly for portable, power hand tools, and in thisrespect in particular for grinding machines. A clamping fixture of thistype has been disclosed (German Patent Specification 3,012,836) in whichone flange, which is arranged on the side of the tool pointing towardsthe housing of the power hand tool, is axially movable relative to thespindle and designed as a driving plate. This rear supporting flange iscoupled to the spindle in such a way as to transmit torque and isaxially supported in an end position on a shoulder of this spindle. Theother flange, which can be screwed onto the end of the spindle, consistsof a nut having a separate clamping element which is roughly pot-shapedin cross-section and is supported axially against the flange of theclamping nut via a coil spring. When this clamping nut is screwed on andtightened, the pot-shaped clamping element is pressed axially againstthe tool via the axially compressed spring, and the tool is therebytightened against the flange on the spindle side, the end face of acylindrical extension of the clamping nut coming to bear directly on afacing axial side of the rear flange and, during further tightening ofthe clamping nut, this rear flange on the spindle side being tightenedtogether with the clamping nut, if necessary until the rear flange comesto bear axially on the shoulder surface of the spindle. In an anglegrinder, the grinding disc is thereby supposed to be mounted with adefined contact pressure and this contact pressure is supposed to beensured. This clamping fixture is also intended to enable a quick andsimple interchange of the grinding disc and at the same time avoidoverloading of the power hand tool, in particular the angle grinder.This is because, if the torque acting on the grinding disc is too great,the grinding disc stops, while the rear flange and also the clamping nuthaving the clamping member, perform a relative movement thereto. Theeffect of the clamping nut automatically tightening further inoperation, makes it considerably more difficult to loosen the clampingnut when changing the grinding disc. Therefore loosening of the clampingnut is here only possible with the assistance of a special auxiliarytool, the spindle, depending on the design of the machine, having to beappropriately counterheld by a second auxiliary tool, e.g., a spanner.

SUMMARY OF THE INVENTION

The object of the invention is to provide a clamping fixture in which atool change is possible without any auxiliary tool, which tool change,in addition, can be performed quickly and safely. The clamping fixtureis shifted from the front area, exposed when used as specified, into thearea between tool and bearing flange of the housing so that any risk ofdamage, e.g. chafing on the work piece, is countered. Furthermore, theclamping fixture is simple and robust in construction as well asadequately protected against dirtying from the outside. Any wear offunctionally important parts is taken into account. Simple and easytwo-hand operation is achieved. The front clamping nut is taken overunchanged in a known manner so that recourse can be made here tostandardised, cost-effective parts. At the same time, it is stillpossible in especially stubborn cases, e.g. in the event of a rusted-inclamping nut, for a spanner to be placed thereon, and the clamping nutcan be released with this auxiliary tool. The supporting flange is in arotationally fast positive-locking connection with the spindle so thatrelevent regulations are complied with. In addition, the supportingflange is removably attached, which further facilitates the tool change.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction so to its mode ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of preferredembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic axial longitudinal cross-sectional view of afirst embodiment of a clamping fixture according to the presentinvention as part of an angle grinder having a mounted grinding disc,

FIG. 2 shows a schematic sectional view along line II--II in FIG. 1 of adetail of the clamping fixture,

FIG. 3 shows a schematic axial longitudinal cross-sectional view roughlycorresponding to that in FIG. 1 of a second embodiment of a clampingfixture according to the present invention,

FIG. 4 shows a developed side view of detail IV in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows the lower part of a portable power hand toolwhich is designed, for example, as an angle grinder and has a spindle 10which is motor-driven via a gearing and is supported in housing 11 atone end by a needle bearing 12 and, at an axial distance therefrom, by aball bearing 13. The inner ring of the ball bearing 13 is axiallysupported on a shaft collar 14. At the end, the spindle 10 is providedwith a threaded portion 15 which has an external thread 16. The spindle10 serves to drive a tool 17 which consists, for example, of thegrinding disc as shown or another tool disc, e.g. a cup wheel, brush, arubber plate or the like. The tool 17 is detachably fixed on the spindle10 by a clamping fixture. The clamping fixture has two flanges 18 and 19between which the tool 17 can be clamped axially in place. One flange 19is formed by a clamping nut 20 which has a hub part 21 and a throughinternal thread 22 with which the clamping nut 20 is screwed onto theexternal thread 16. The tool 17, during fixing, is centred on the outerperipheral surface of the hub part 21.

The other flange 18 forms a mating flange. It is held in an axiallydisplacable manner on the spindle 10 and in the process is coupled tothe spindle 10 in such a way as to transmit torque. Used for thispurpose is a slot-and-key connection having a Woodruff key 23 which isaccommodated in a positive-locking manner in the spindle 10 and engagesinto an axial through groove 24 of the flange 18.

On the axial side of the flange 18 remote from the tool 17, a supportingelement is arranged on spindle 10 so as to be movable relative thereto,which supporting element consist of an annular part 25 and is heredesigned as a nut 26. The nut 26 is located at least a slight axialdistance from the flange 18. It has an internal thread 27 with which itis movable on the thread on a threaded portion 28 of the spindle 10. Theexternal thread of the threaded portion 28 and the internal thread 27 ofthe nut 26 are each designed as right-hand coarse threads whose leadangle is selected to be of such a size that the coarse in the reliableself-locking range.

Arranged axially between the flange 18 and the nut 26 is an axial ballbearing 29 via which the flange 18 is supported axially on the nut 26.

Placed between the flange 18 and the nut 26 is a torsion spring 30 whichacts with one leg end 31 on the flange 18 and with its other leg end 32on the nut 26. The nut 26, via the coarse thread of the threaded portion28, is pressed against the axial ball bearing 29 by the force of thetorsion spring 30. This axial screw force is transmitted to the flange18 whose axial displacement in the direction away from the nut 26 islimited by a stop 33 in the form of a snap ring on the spindle 10.

An axial movement of the nut 26 relative to the spindle 10 and in thedirection away from the flange 18 is limited by the shaft collar 14 ofthe spindle 10.

Fixed to the flange 18 is a cylindrical protection sleeve 34 whichextends axially over at least an area of both the flange 18 and the nut26 and as a result protectively covers in this area the flange 18, thenut 26 and axial intermediate area between the two. The protectionsleeve 34 provides the radial support to the outside for theunrestrained balls of the axial ball bearing 29 and at the same timeseals off to the outside the area between the nut 26 and the flange 18.The protection sleeve 34 overlaps the nut 26 axially with clearance formovement so that it does not prevent the relative movement of the nut 26relative to the spindle 10 plus flange 18.

In addition, arranged on axial side of the nut 26 remote from the flange18 are two sealing rings 35, 36, of which one 35 is held on the nut 26and the other 36 is held on a part of the bearing flange 37 of thehousing 11. The two sealing rings 35, 36 together form a doublelabyrinth and protect the axial ball bearing 29 and the coarse thread ofthe threaded step 28 as well as the internal thread 27 of the nut 26from dirt.

A locking device 38 accessible and operable from outside is allocated tothe nut 26. This locking device 38 has a thrust bolt 40 which is loadedby a spring 39, is reset into the inactive disengagement position and isheld and guided in a guide 41 of the bearing flange 37 so as to beradially displacable in a translatory manner with regard to the spindle10. At the end on the inside, the thrust bolt 40 carries a lockingmember 42 which, when the locking device 38 is actuated, can prevent thenut 26 from turning. The locking member 42 here consists of a roughlystrip-like finger 43 angled at the lower end. This finger 43 is securedagainst tilting or turning about the axis of the thrust bolt 40 andguided in a guide 44. The guide 44 is formed, for example, by twoadjacent ribs 45, 46 of the housing 11. Recesses 47, 48 adjacent to theribs 45, 46 ensure that the translatory movement of the finger 43,triggered by displacement of the thrust bolt 40, is not blocked, forexample by dirt or such like trapped impurities.

On the outside, the nut 26 has at least one, conveniently a plurality ofcatch openings 49, 50 which are arranged at equal circumferentialangular distances from one another, are open to the outside and towardsthe finger 43 and are adapted to the dimensions of the finger 43 in sucha way that the finger 43 fits into the catch openings 49, 50 when thethrust bolt 40 is pressed in a direction of arrow 51 by hand.

If the tool 17 is to be removed and changed, the thrust bolt 40, whenthe motor is switched off, is pressed by one hand from the outside inthe direction of arrow 51 up to the stop, and the other hand takes holdof the tool 17 and rotates the latter together with the clamping fixtureincluding the flange 18, the spindle 10 and nut 26 until the finger 43engages into a catch opening 49 or 50 moving into its area, whereuponthe nut 26 is prevented from turning during this rotation. The thrustbolt 40 is then held by hand in this engaged position. At the same time,the other hand exerts a torque on the tool 17 in anti-clockwisedirection. This torque is transmitted by the tool 17 via the flanges 18,19 to the spindle 10 and its threaded step 28 having a coarse thread. Ifthe torque exerted by hand in this manner now becomes greater than thefriction moment in the coarse thread including the torque of the torsionspring 30, the nut 26 is released from its axial contact with the axialball bearing 29 and, during further rotation, is displaced axially in adirection away from the flange 18 up to the stop at the shaft collar 14.Consequently, the axial ball bearing 29 and with it the flange 18 becomefreely movable axially so that the clamping pressure effective betweenboth flanges 18 and 19 and clamping the tool 17 in place drops and theclamping nut 20 is relieved. The latter can now be fully unscrewed fromthe threaded step 15 by hand and then the tool 17 can be replaced.

The release moment at the periphery of the tool 17 is dependant upon thelead angle of the coarse thread on the threaded step 28 and the nut 26.The greater the lead angle, the smaller the release moment. This leadangle is established in such a way that the coarse thread of thethreaded step 28 and the internal thread 27 of the nut 26 lie in thereliable self-locking range, and in fact while allowing for the torqueof the torsion spring 30, which torque counteracts the release moment.

If the tool 17 has been exchanged for another and if this other tool isto be clamped, the locking device 38 is again actuated by hand in themanner described above so that the finger 43 engages into a catchopening 49, 50 of the nut 26. The clamping nut 20 is screwed down gentlywith the other hand and thus the new tool 17 is likewise gentlytightened. This is sufficient, since, when the motor is subsequentlyswitched on, the tool 17 tightens automatically in operation.

The axial ball bearing 29' arranged between the nut 26 and the flange18' has the advantage that the surface friction between the two is thusreduced to a rolling friction and is thus virtually negligibly small.

The clamping fixture described has manifold advantages. It lies in theprotected area between the tool 17 and the bearing flange 37 extendingthereabove, and the risk of any damage or impairment when using thepower hand tool as specified is completely averted. What is more,reliable protection against dirt, dust and other contaminants isobtained by simple means. The clamping fixture is simple and robust inconstruction. Any wear of functional parts of this fixture is reduced toa minimum or even eliminated completely. The clamping fixture isexceptionally simple, cost-effective and quick, safe and easy to handle.It enables the tool 17 to be quickly and safely changed withoutrequiring any additional special tools for this purpose. Simple and easytwo-hand operation is achieved. In the process, the standardisedclamping nut 20 present in other machines will be retained unchanged, aswill a rotationally fast, positive-locking connection between the flange18 supporting the tool 17 and the spindle 10. Thus correspondingrelevant regulations are complied with. In addition, it is advantageousthat the flange 18 is mounted undetachably on the spindle 10. Theclamping fixture is not restricted to grinding discs such as tool 17. Onthe contrary, other tools, e.g. cup wheels, brushes, rubber plates orthe like can be also be clamped without auxiliary tool.

Locking devices for the spindles of angle grinders are known per se. Inknown power hand tools, however, these locking devices are located inthe gearing space. The design according to the invention differstherefrom in that the locking device 38 is instead arranged in the areaof the bearing flange 37 and the ball bearing 13. This shifting of thespindle-locking device has the advantage that sealing problems do notoccur and, furthermore, catch openings necessary at the crown wheel forthe positive locking of the spindle are dispensed with, as a result ofwhich the crown wheel comes substantially cheaper and also theconfiguration of the housing 11 becomes simpler and more cost-effective.In addition, the stress on the individual parts of the spindle-lockingdevice is substantially reduced. During release, the stress is, forexample, only about 6% of that of any other known spindle-lockingdevices. The advantage of the lateral arrangement of the thrust bolt 40accessible from outside is also retained here in the locking device 38according to the invention. Each time before the tool 17 is clamped thenut 26 is positively returned into the initial position via the lockingdevice 38.

In the second embodiment shown in FIGS. 3 and 4, reference numeralsincreased by 100 are used for the parts which correspond to the firstembodiment so that reference is thereby made to the description of thefirst embodiment to avoid repetitions.

The second embodiment differs from the first embodiment in that theannular part 125 which serves as supporting element for the flange 118consists of a disc 152 which is displacable and rotatable relative tothe spindle 110. The spindle 110, instead of being provided with thethreaded portion 28 as in the first embodiment, is provided in this areawith a continuous cylindrical outer peripheral surface.

The axial ball bearing arranged axially in the first embodiment betweenthe annular part 25 and a nut 26 is omitted in the second embodiment.Arranged instead on the axial side of the disc 152 remote from theflange 118 is a schematically indicated axial ball bearing 153 on whichthe disc 152, with the facing axial side, is supported. The axial ballbearing 153 is in turn supported on the shaft collar 114 of the spindle110.

The cylindrical protection sleeve 134 is here firmly attached to thedisc 152. It covers an axial part of the flange 118 and does this withclearance for movement. As in the first embodiment, the disc 152 and theflange 118 are coupled by the torsion spring 130.

As apparent in particular from FIG. 4, both the disc 152 and the flange118, on the end faces axially facing one another, have, e.g., threesloping surfaces 152a and 118a respectively, which follow one another atdistances in the peripheral direction and are inclined to the left. Thesloping surfaces 152a, 118a are axial wedge surfaces with which theflange 118 and the disc 152 bear axially against one another, as followsfrom the developed view according to FIG. 4.

In this arrangement, the wedge angle α of these sloping surfaces 152a,118a is selected to be of such a size that it lies in the reliableself-locking range.

The torsion spring 130, which, as in the first embodiment, is supportedwith one leg end 132 on the disc 152 and with its other leg end 131 onthe flange 118, rotates the disc 152 and the flange 118 relative to oneanother in such a way that both parts slide up on the sloping surfaces118a, 152a and are thereby move apart axially. This axial spreadingmovement is limited in one direction by the shaft collar 114 and in theother direction by the stop 133 in the form of the snap ring of thespindle 110.

If the tool 117 is to be removed and changed, first of all, as has beendescribed for the first embodiment, the disc 152 is rotationally lockedby the locking device 138, which is designed just as in the firstembodiment. If the tool 117 is then rotated anti-clockwise by the otherhand, the flange 118 and the spindle 110 are also driven along in theprocess. The rotation of the flange 118 anti-clockwise causes thesloping surfaces 118a of the flange 118 to slide towards the wedgebottom of the sloping surfaces 152a of the rotationally locked disc 152,which leads to corresponding axial relief, whereupon the clamping nut120 becomes loose and can easily be unscrewed fully by hand. The slidingmovement of the flange 118 with the sloping surfaces 118a towards thewedge bottom of the sloping surfaces 152a is limited by locking surfaces154 of the disc 152 and 155 of the flange 118, which locking surfaces154 adjoin the sloping surfaces and are directed axially towards oneanother. These locking surfaces 154, 155 form dog steps.

As soon as the releasing torque is reduced to zero when the tool 17 isbeing released, the torsion spring 130 is able to rotate the flange 118relative to the disc 152 so that the sloping surfaces 118a of the flange118 slide towards the wedge top on the sloping surfaces 152a of the disc152, as a result of which the two parts 152, 118 are again thrust apartaxially. The tool 117 is clamped in the thrust-apart position.

In another embodiment (not shown) rolling bodies are located between thesloping surfaces 118a, 152a, as a result of which the surface frictionbetween the sloping surfaces 118a, 152a is further reduced.

While the invention has been illustrated and described as embodied in aclamping fixture for detachably fixing a disc-type tool, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A clamping fixture for detachablyfixing a discs-like tool to a driven spindle having a threaded portionwith an external coarse thread, said clamping fixture comprising aflange for applying a clamping force to the tool, said flange beingaxially displaceable relative to the driven spindle and coupled with thedriven spindle in a torque transmitting relationship; a supportingelement for supporting said flange and displaceable relative to saidspindle to prevent said flange from applying a clamping force to saidtool, said supporting element comprising an annular nut memberdisplaceably mounted on the spindle adjacent an end of said flange whichis remote from the tool, and having a coarse thread to be screwed ontothe threaded portion with an external coarse thread of the spindle; atorsion spring for directly coupling said annular nut member with saidflange and having opposite ends connected to said annular nut member andsaid flange, respectively; and a locking device including a lockingmember for preventing rotation of said annular nut member upon actuationof said locking device.
 2. A clamping fixture according to claim 1,wherein a lead angle of a coarse thread is so selected that it lies in areliable self-locking range of the coarse thread.
 3. A clamping fixtureaccording to claim 1, further comprising an axial bearing locatedbetween said flange and said annular nut member.
 4. A clamping fixtureaccording to claim 3, wherein said axial bearing is a ball bearing.
 5. Aclamping fixture according to claim 1, wherein the spindle has a collar,said annular nut member comprising a disc portion axially displaceableand rotatable relative to the spindle, said clamping fixture comprisingan axial bearing for supporting said disc portion on the collar of thespindle.
 6. A clamping fixture according to claim 5, wherein saidbearing is a ball bearing.
 7. A clamping fixture according to claim 1,further comprising a slot-and-key connection for coupling said flange tothe spindle.
 8. A clamping fixture according to claim 1, furthercomprising stop means for limiting axial displacement of said flange ina direction away from said annular nut member.
 9. A clamping fixtureaccording to claim 8, wherein said stop means for limiting axialdisplacement of said flange comprises a snap ring to be secured to thespindle.
 10. A clamping fixture according to claim 1, further comprisingstop means to be secured to the spindle for limiting axial displacementof said annular nut member relative to the spindle.
 11. A clampingfixture according to claim 10, wherein said stop means for limitingaxial displacement of said annular nut member relative to the spindlecomprises a collar having an end surface which is opposite to an endsurface of said collar facing said annular nut member and which servesas a stop for a ball bearing supporting the spindle in a housing of apower hand tool.
 12. A clamping fixture according to claim 1, furthercomprising a cylindrical protective sleeve extending axially over anarea including at least portions of said flange and said annular nutmember for covering respective portions of said flange and said annularnut member and an axial intermediate area threrebetween.
 13. A clampingfixture according to claim 12, wherein said cylindrical protectivesleeve is fixed to one of said flange and said annular nut member andaxially overlaps with a clearance a respective portion of the other ofsaid flange and said annular flange member.
 14. A clamping fixtureaccording to claim 1, further comprising two sealing rings arranged onan axial side of said annular nut member which is remote from saidflange to form a double labyrinth thereat.
 15. A clamping fixtureaccording to claim 1, wherein said locking device includes aspring-loaded thrust bolt transversely displaceable in a power toolhousing.
 16. A clamping fixture according to claim 15, wherein saidthrust bolt has an inner end carrying said locking member.
 17. Aclamping fixture according to claim 16, wherein said annular nut memberhas a catch opening facing said locking member, said locking membercomprising a finger engaging in a positive-locking manner said catchopening upon actuation of said locking device.
 18. A clamping fixtureaccording to claim 17, wherein a housing of a power hand tool has aguide for guiding said finger, said finger being secured againstrotation.